SShape.java

package libai.fuzzy.sets;

import org.w3c.dom.Node;

/**
 * Fuzzy set representing a S-shape function. This function will equal 0 for any
 * value to the left of a, and 1 for any value to the right of b. This function
 * is a mirror of the Z-shape.
 *
 * @author kronenthaler
 */
public class SShape extends TwoParameterSet {

    public SShape(Node xmlNode) {
        load(xmlNode);
    }

    /**
     * Constructor.
     *
     * @param a Left value of the S-shape.
     * @param b Right value of the S-shape.
     *
     */
    public SShape(double a, double b) {
        this.a = a;
        this.b = b;
    }

    @Override
    public double eval(double x) {
        if (x <= a) {
            return 0;
        }
        if (x >= b) {
            return 1;
        }

        if (x >= a && x <= (a + b) / 2) {
            return 2 * Math.pow((x - a) / (b - a), 2);
        }

        return 1 - (2 * Math.pow((x - b) / (b - a), 2));
    }
}